Wonderful mod, ingenious was to create extra storage, but with what I know about surface plates and half ton weights, I don't think I'd
rely on a 18ga. sheet metal base. That's only ~.020". Not too sure about that. Gut feeling is that it's flimsy.
Tooling up an ordnance project back in the 80's I ordered (3) 4'x8' Starrett Pinks. They sat on massive bases, ever the 4'x4's ones did.
The large Pinks came in totally out of spec and had to be reworked. Took a couple of weeks, moving them into the Met Lab, letting them
soak and than lapping and bringing them into spec. I was very surprised they came in that far off-spec.
If you have a temperature change of a couple of degrees, the steel changes and you're back to square one waiting on the steel to stabilize.
I need to watch his videos later on when he laps it. I want to see the method used to get 'lab' grade specs in a garage.